Scanning apparatus linearization and calibration system

ABSTRACT

The scanning apparatus linearization and calibration system includes an electromechanical scanner having a sample stage portion, and a deflecting member, mounted between the scanning means and a fixed mounting member, that undergoes deflection in response to displacement of the scanner sample stage portion in at least one dimension of displacement. Strain gauges are mounted to the deflecting member for measuring the deflection of the deflecting member and for generating a deflection output signal indicative of an amount of deflection of the deflecting member, to provide a highly sensitive indication of actual displacement of the sample stage of the scanning apparatus. Control circuitry also provides for open loop displacement correction and for closed loop feedback correction of the position of the scanner sample stage.

This is a continuation of application Ser. No. 08/357,133, filed Dec.15, 1994, (now U.S. Pat. No. 5,469,734), which is a continuation of Ser.No. 07/979,762, filed Nov. 20, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to linearization and calibration ofelectromechanical scanning devices, and more particularly relates to anapparatus for position measurement of a sample scanning stage used withscanning microscopes and surface measurement systems.

2. Description of Related Art

Devices for producing precise linear, two or three dimensional motionhave proven to be highly useful in scanning devices. In particular,electromechanical transducers such as piezoelectric ceramic actuators,which expand upon being subjected to an electrical potential, have beenused for X-Y-Z positioners in scanning probe microscopes. Suchpiezoelectric ceramic materials have been combined in laminates, tubes,or stacks, to allow two-dimensional and even three-dimensional motion ofthe sample stages for such systems.

Piezoelectric ceramic actuators are electromechanical elements thatundergo dimensional changes about a poling axis which has been formed inthe material during the manufacturing process. When an electrical fieldis applied to the ceramic, the material generally expands about thepoling axis and contracts perpendicular to the poling axis. However, thedimensional response of such piezoelectric materials to an appliedvoltage is not linear, and such materials commonly display varyingdegrees of hysteresis, creep, and a variable sensitivity to applicationof voltage. Hysteresis occurs due to a difference in dimensional changesin response to an applied voltage, depending upon whether the voltage isan increase or decrease from the previous applied voltage. Although thedegree of hysteresis and non-linearity of response is less for hardpiezoelectric materials (having a Curie temperature above 300° C., andproducing smaller displacements) than for soft piezoelectric materials(having a Curie temperature below 200° C., and producing largerdisplacements), the hard piezoelectric material still typically has adegree of hysteresis on the order of 2%, and a deviation from linearityof about 1%. Creep is a phenomenon of temporary dimensionalstabilization which occurs after application of a step change in voltageto cause an initial dimensional change, followed by a gradual, longterm, small dimensional change in the direction of the initial change.The amount of creep for a piezoelectric material can range from 1% to20% of the initial dimensional response over a period of about 10 to 100seconds.

Scanning probe microscopes such as scanning force microscopes, alsoknown as atomic force microscopes, are useful for imaging objects assmall as atoms. The scanning force microscope is closely related to thescanning tunneling microscope and the technique of stylus profilometry.In a typical scanning force microscope, a laser beam is directed at areflective portion of a lever arm carrying a probe so that a verticalmovement of a probe following the contours of a specimen is amplifiedinto a relatively larger deflection of the light beam. The deflection ofthe laser beam is typically monitored by a photodetector array in theoptical path of the deflected laser beam, and the sample is mounted on asample stage moveable in minute distances in three dimensions so thatthe sample can be raster scanned while the vertical positioning of theprobe relative to the surface of the sample is maintained substantiallyconstant by a feedback loop with the photodetector controlling thevertical positioning of the sample. Such scanning force microscopes areuseful for imaging a sample which is moved in three dimensions while thesensor head is stationary and separate from the scanning assembly movingthe sample. Alternative constructions in which the sample is heldstationary while the probe is moved may also be used to accomplishessentially the same results.

Scanning force microscope images can be severely distorted due toproblems of hysteresis, creep, and generally non-linear response ofpiezoelectric materials used in scanning devices for such microscopes.In view of the high resolution and positioning accuracy required toavoid distortions in scanning force microscope imaging, it would bedesirable to provide an electromechanical scanning apparatus whichinsures precise translational motion of the scanning device and accuratemeasurement of the position of the probe relative to the sample.

Distortions in scanner displacement of an X-Y-Z scanner have beentypically corrected by closed loop feedback correction or postimagingsoftware, based upon determination of corrected (x,y) positionsaccording to a formula with a number of variables, and variousstrategies for interpolation, or based upon measurements of the actualscanner displacement. Correction by postimaging software can be timeconsuming and require a high utilization of computing resources; andinterpolation errors in the process can blur and distort the image.Linear-variable differential transformer, optical interferometry,capacitance, and optical beam position sensing methods have also beenused for measuring actual scanner displacement. Interferometry hasproven to be very accurate, but results in a periodic output function,and is complex to implement. A photoelectric differencing system, with apredetermined dynamic range, has also proven useful, but has a limitedresolution capability. Strain gauges that change their electricalresistance with a change in length are sensitive indicators that can bebonded directly to piezoelectric actuators to give an indication oflocalized extension of the actuator, which can in turn be used toextrapolate approximate displacement of a stage. However, mounting thestrain gauges directly on the ceramic does not work well when the scanrange is greater than approximately 1 micron (μ).

It would be desirable to provide an improved system for linearizing andcalibrating non-linear electromechanical scanning devices having greaterthan 1μ of extension, with improved linearity over conventional methods,thereby reducing problems of hysteresis, creep and non-lineardisplacement responses. It would also be desirable to provide such animproved system that is small and relatively inexpensive to manufacture.The present invention meets these needs.

SUMMARY OF THE INVENTION

Briefly and in general terms, the scanning apparatus linearization andcalibration system according to the present invention provides forimproved X-Y-Z positioning and imaging accuracy for high resolutionmicroscopes and provides a means to reduce problems of hysteresis,creep, and non-linear sensitivity of scanner apparatus electromechanicalactuators known in the art. The system of the invention provides anelectromechanical scanning apparatus having a sample stage portion, adeflecting structure mounted between the scanning apparatus and thefixed mounting base so that the deflecting structure undergoesdeflection in response to displacement of the scanning apparatus portionin at least one dimension of displacement, and means for measuring thedeflection of the deflecting structure and for generating a deflectionoutput signal indicative of an amount of deflection of the deflectingstructure. In a preferred embodiment, strain gauges are mounted to thedeflecting structure to provide a highly sensitive indication of actualdisplacement of the sample stage of the scanning apparatus, for improvedlinearity and calibration, with a greater dynamic range than heretoforeprovided by conventional methods. The improved scanning apparatuslinearization and calibration system of the present invention is alsosmall and relatively inexpensive to manufacture and does notsubstantially complicate the construction of the scanning system.

In a currently preferred embodiment of the invention, the apparatusprovides a scanning apparatus linearization and calibration systemcomprising a fixed mounting base, and scanning means having a scanningprobe apparatus suitable for use with a scanning force microscope orscanning tunnelling microscope. The scanning probe apparatus is mountedto the fixed mounting means for displacement in at least one dimensionof displacement relative to the fixed mounting base. In one preferredembodiment, the scanning apparatus comprises a translation stage towermounted to the fixed mounting base for pivotal movement, and in a secondpreferred embodiment, the scanning apparatus comprises a piezoelectrictube scanner mounted to the fixed mounting base. A control system isalso provided for generating a command signal for a desired displacementof the scanning apparatus in at least one dimension of displacement. Inpreferred embodiments, the control system generates a plurality ofcommand signals for desired displacement of the scanning apparatus intwo or three dimensions of displacement. An electromechanical actuatorelectrically connected to the control system is mounted to the fixedmounting base for displacing the scanning apparatus sample stage portionin up to three dimensions of displacement relative to the fixed mountingbase responsive to command signals. A deflecting member such as a beamis mounted between the scanning apparatus and the fixed mounting baseand undergoes deflection corresponding to displacement of the scanningapparatus sample stage portion in at least one dimension ofdisplacement.

In one preferred embodiment, first and second deflecting members aremounted between the scanning apparatus and the fixed mounting base.Means are also provided for measuring the deflection of the deflectingmember and for generating a deflection output signal indicative of anamount of deflection of the deflecting member, and in a preferredembodiment, the means for measuring the deflection comprises at leastone strain gauge mounted to the deflecting member for producing anelectrical signal indicative of the amount of deflection of thedeflecting member. In a preferred implementation, at least one set offirst and second strain gauges are mounted on opposing sides of adeflecting beam for producing first and second electrical signalsindicative of the amount of deflection. The first and second electricalsignals are preferably connected to a differential amplifier having anoutput proportional to the actual displacement of the scanning apparatusrelative to the fixed mounting member from a position in which thedeflecting beam is undeflected, or from a position in which thedisplacement of the sample stage is substantially zero, where thedeflecting member is prestressed to a slight degree. The strain gaugesare also preferably connected in a temperature compensated bridgeconfiguration. Means are provided for determining an actual displacementof the scanning apparatus sample stage in at least one displacementdimension electrically connected to the means for measuring thedeflection based upon the output deflection signal, and for determininga displacement correction in at least one dimension of displacement bycomparing the desired displacement with the actual displacement. In apreferred embodiment, the scanner apparatus linearization andcalibration system includes closed loop feedback control means forintegrating the displacement correction to provide an integrateddisplacement correction signal, and means for modifying the commandsignal with the integrated displacement correction signal to produce thedesired displacement of the scanning means.

In a presently preferred embodiment, the method of the inventioninvolves inputting a signal to one or more piezoelectric actuators whichhas been predetermined to drive the actuator to a desired location, thuspositioning the sample stage attached to the actuator. The actuator isalso connected to a deflecting member, such as a beam, which is alsoattached to a base member. One or more strain gauges are mounted on thedeflecting member to provide an output proportional to the strain on thesurface of the deflecting member and thus related to the displacement ofthe deflecting member. The output of the strain gauge(s) may be used asa feedback signal to correct the input signal to the piezoelectricstack, or as a direct readout of displacement for one or more axes.

In another preferred embodiment of the invention, the measurement probeis scanned relative to the sample, which may also be either capable ofbeing scanned or fixed. In such an embodiment, the deflecting membersuch as a beam or resilient element or structure is mounted between theprobe and a fixed base and is equipped with one or more strain gauges tomeasure the deflection of the deflecting member. The output of thestrain gauges may be used to measure the position of the probe and alsomay be used as an input to control the movement of the probe by afeedback control system driving the probe displacement actuators.

From the above, it may be seen that the present invention represents asubstantial improvement in the ability to measure the position of probesin scanning probe systems without substantially increasing the cost orcomplexity of the scanning system. Other aspects and advantages of theinvention will become apparent from the following detailed description,and the accompanying drawings, which illustrate, by way of example, thefeatures of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the scanning apparatuslinearization and calibration system of one embodiment of the invention;

FIG. 2 is a top plan view of the system shown in FIG. 1, rotated 45°clockwise;

FIG. 3 is a cross-sectional view of the system of the invention takenalong line 3--3 of FIG. 1, rotated 45° clockwise;

FIG. 4 is a simplified schematic diagram of the closed loop feedbackcontrol system of the invention;

FIG. 5 is a schematic diagram of an integral feedback loop of the closedloop feedback control system of FIG. 4;

FIG. 6 is a side elevational view of an alternate embodiment of thescanning apparatus linearization and calibration system of theinvention;

FIG. 7 is a top plan view of the system shown in FIG. 6;

FIG. 8 is a cross-sectional view of the system of the invention takenalong line 8--8 of FIG. 6;

FIG. 9 is a simplified schematic diagram of the closed loop feedbackcontrol system of the invention for use with a tube scanner; and

FIG. 10 is an elevational view of the system of FIGS. 6-8 with anadjustable tensioner device.

FIG. 11 is a perspective view of an arrangement in which the inventionis used on both a scanning stage and probe motion actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is shown in the drawings, which are included for purposes ofillustration, but not by way of limitation, the invention is embodied inan electromechanical scanning apparatus linearization and calibrationsystem such as is suitable for positioning a sample stage such as may beused with high resolution microscopes such as scanning force microscopesor scanning tunneling microscopes, or the like, in up to threedimensions, for relative positioning of a sample stage relative to asensor probe of the microscope. Such microscopes are useful for imagingobjects as small as atoms, so that there is a need for a stabletranslational positioning apparatus capable of positioning an objectwith extremely high resolution in up to three dimensions with a minimumof linear or rotational error.

With reference to FIGS. 1-3, in one preferred embodiment, the scanningapparatus linearization and calibration system 10 includes a flat planarbase member 12, having a bottom portion 11 with mounting holes 13 formounting of the base member to a platform (not shown) for the scanningapparatus. The base member includes fixed mounting wall plates 14aextending perpendicular to the bottom portion of the base member. Apivoting scanning tower 16 with a sample stage 18 at one end is mountedto the base member for pivotal movement relative to the base member,preferably by a threaded bolt connection 20, extending through a pivotwell portion 22 in the bottom portion of the base member. The samplestage may comprise a magnetic material, to allow a specimen to bemounted by adhesion onto a small magnetic steel plate which can thus bemagnetically secured on the top of the stage, allowing for theconvenient interchange of specimens to be examined by the instrument.

A control unit 24 is electrically connected to electromechanicalactuators 26a,b,c for pivotally translating the sample stage of thescanning tower in x and y dimensions of a horizontal plane, and forvertically controlling the position of the sample stage in a zdimension, respectively, via control lines 28. The control unitpreferably generates command signals for driving the electromechanicalactuators in all three dimensions for linear, or two or threedimensional translation of the sample stage. The electromechanicalactuators preferably comprise piezoelectric ceramic actuators whichexpand upon being subjected to an electrical current, typically formedof piezoelectric ceramic materials that have been combined in laminatesor stacks. Actuators 26a and 26b are preferably mounted at right anglesto each other between the fixed mounting wall plate of the base memberand the scanning tower control the pivotal, as is best seen in FIG. 3,for translation of the sample stage in the horizontal orthogonal x and ydimensions. The actuator 26c is preferably mounted within the pivotingscanning tower between the base of the scanning tower and the samplestage, for raising the sample stage vertically in a z directionorthogonal to the x and y dimensions.

A pair of deflecting members 30 are preferably mounted between thescanning tower and the fixed mounting wall plate above theelectromechanical actuators to undergo deflection in response to andcorresponding to displacement of the sample stage of the scanning towerin the horizontal x and y dimensions of displacement. In one preferredembodiment, each deflecting member comprises an elongated beam mountedbetween the fixed mounting wall plate and the pivoting scanning tower,although the deflecting member can alternatively comprise otherdeflectable material and configurations, such as an elastic structure,or the like. The deflecting members are also preferably prestressed tohave a slight degree of curvature in an initial position in which thescanning tower and sample stage have undergone substantially zerodisplacement by the electromechanical actuators.

At least one strain gauge 32 of the type known in the art, such as thinsemiconductor or thin metal film strain gauges having a resistance thatchanges in proportion to their change in length, is mounted on each ofthe deflecting members, for producing an electrical signal indicative ofthe amount of deflection of the deflecting members. Two sets of straingauges are preferably mounted in pairs on opposing sides of each of thedeflecting members, for producing first and second electrical outputdeflection signals corresponding to each of the x and y dimensions,indicative of the amount of deflection of the deflecting members, andthereby the amount of displacement of the sample stage in the x and ydimensions. The strain gauges are electrically connected by lines 34 tothe control unit for measuring resistance of strain gauges fordetermining deflection of the deflecting members. The output deflectionelectrical signals from the pairs of strain gauges are preferablyreceived by a differential amplifier having a differential outputdeflection signal proportional to the actual displacement of the scannersample stage relative to the fixed mounting member from a position inwhich the deflecting member is undeflected, or from a position in whichthe displacement of the sample stage is substantially zero, where thedeflecting member is prestressed with a slight degree of curvature.Since such strain gauges are also very sensitive to changes intemperature, the strain gauges are also preferably connected in atemperature compensated bridge configuration. Alternatively, it wouldalso be possible to mount an intermediate deflecting member with straingauges attached between each electromechanical actuator and the pivotingscanner tower, since the amount of displacement of the scanner samplestage can be correlated with the amount of deflection of such anintermediate deflecting member, provided the strain gauges aresufficiently sensitive.

The control unit preferably includes a scan generator circuit 35 togenerate a command signal 36 for driving each of the electromechanicalactuators. The control unit also preferably includes means fordetermining an actual displacement of the scanning means sample stage inat least one displacement dimension, such as an output deflection signalto voltage converter 37 electrically connected to the strain gauges forreceiving the electrical output deflection signals, to output a positioncorrection signal 38, representing the actual displacement of thescanner sample stage. The position correction signal can be receiveddirectly by a memory means 39 for recording the actual (x,y) positionsof the scanner sample stage along with the readings of the microscopeinstrument at those positions, for linearization of image data bypostimaging correction techniques, or for calibration of commandedpositions by the recorded actual (x,y) positions of the scanner forfuture scans, according to conventional techniques. In an alternativepreferred embodiment illustrated in FIG. 4, a differential amplifier 40can be electrically connected to receive the position command signal 36and the actual position correction signal 38 to output a correctedcommand signal to the electromechanical actuators in a closed feedbackloop configuration.

An alternate form of a closed feedback loop configuration is alsoillustrated in FIG. 5, in which the output of the scan generator 35 ofthe control unit and the output of position sensors 44 are summed atsumming junction 46, to provide a summed signal received by a firstintegrator 48 and a differentiator 50. The output of the firstintegrator 48 is received by a second integrator 52 and summing junction54, which also receives output from the second integrators 52 and thedifferentiator 50, to provide closed loop, double integration feedbackto the electromechanical actuator 56.

An alternate preferred embodiment of the invention is shown in FIG. 6-8,illustrating a tube scanner linearization and calibration system 60. Thesystem 60 includes a flat planar base member 12 with mounting holes 63for fixedly mounting the base member to a platform (not shown) for thescanning apparatus. A scanning x-y tube, or tube scanner 64 preferablyincludes four vertical, individually actuatable electromechanicalsegments 66abcd formed of piezoelectric material, and is mounted to thebase at its lower end. The tube scanner includes a sample stage 68 atthe upper end, which can be displaced horizontally in orthogonal x and ydimensions by tilting of the tube scanner, and extended vertically inthe z dimension orthogonal to the x and y dimensions, by controlledactuation of the individual segments. The sample stage may comprise amagnetic material, to allow a specimen to be mounted by adhesion onto asmall magnetic steel plate which can thus be magnetically secured on thetop of the stage, allowing for the convenient interchange of specimensto be examined by the instrument.

A control unit 74 is electrically connected to the electromechanicalactuator segments 66abcd for translating the sample stage of thescanning tower in x and y dimensions of a horizontal plane, and forvertically controlling the position of the sample stage in a zdimension, respectively, via control lines 76. The control unitpreferably generates command signals for driving the electromechanicalactuator segments to control the positioning of the sample stage in allthree dimensions for linear, or two or three dimensional translation ofthe sample stage.

A right angle deflecting member 78 having a first elongated uprightportion 79 and a crossbar portion 80 extending at right angles to theupright portion is preferably mounted to the base member at the bottomend of the upright portion and mounted to the tube scanner at the upperend of the crossbar portion. The right angle deflecting member ispreferably formed of elongated deflectable plastic or elastic material,and has orthogonal faces for mounting of at least individual straingauges, and preferably strain gauge pairs 82ab on opposing sides of thedeflecting member, as described earlier. The strain gauge pairs arepreferably mounted on the four orthogonal faces of the upright portionof the deflecting member for detecting displacement of the scannersample stage horizontally in x and y dimensions, and are mounted onupper and lower faces of the upper crossbar member for detectingdisplacement of the sample stage vertically in the z dimension. Theright angle deflecting member is also preferably prestressed duringmounting to the base and scanner to have a slight degree of tension inan initial position in which the scanning tower and sample stage haveundergone substantially zero displacement. It should be noted that thisarrangement of the right angle deflecting member and strain gauges canalso be used interchangeably with the deflecting member and strain gaugeconfiguration illustrated in FIGS. 1-3 for measuring actual displacementof the pivoting scanner sample stage. An optional adjustable tensionermeans 85 may also be mounted to the base member adjacent to the rightangle deflecting member as is illustrated in FIG. 10, for adjusting thestressing and deflection of the deflecting member, for minor adjustmentsof the displacement measurements of the sample stage. Such a tensionermeans may, for example, include a thumbscrew 86 mounted by a bracket 88to the base member. The thumbscrew can be either disposed directlyadjacent to the deflecting member abutting against it, or can operate topress against the deflecting member through an intermediate element.Such an intermediate element can be mounted by a spring element 90 tothe bracket or to the base to allow for a limited range of movement ofthe intermediate element, with a connecting drive member 92 connected tothe spring element and abutting against the deflecting member.

As related earlier with regard to FIGS. 1-3, in the embodimentillustrated in FIGS. 6-8, the strain gauges are electrically connectedby lines 84 to the control unit for measuring resistance of straingauges for determining deflection of the deflecting members. The outputdeflection electrical signals from the pairs of strain gauges arepreferably received by a differential amplifier having a differentialoutput deflection signal proportional to the actual displacement of thescanner sample stage relative to the fixed mounting member from aposition in which the deflecting means is undeflected, or from aposition in which the displacement of the sample stage is substantiallyzero, where the deflecting member is prestressed with a slight degree ofcurvature. Since such strain gauges are also very sensitive to changesin temperature, the strain gauges are also preferably connected in atemperature compensated bridge configuration.

As with the embodiment of FIGS. 1-3, in the embodiment of FIGS. 6-8, andas is illustrated in FIG. 9, the control unit 74 preferably includes ascan generator circuit 35 to generate a command signal 36 for drivingeach of the electromechanical segments of the tube scanner. The controlunit also preferably includes means for determining an actualdisplacement of the tube scanner sample stage in at least onedisplacement dimension, such as the output deflection signal to voltageconverter 37 electrically connected to the strain gauges for receivingthe electrical output deflection signals, to generate a positioncorrection signal 38, representing the actual displacement of thescanner sample stage. The position correction signal can be receiveddirectly by a memory means 39 for recording the actual (x,y) positionsof the scanner sample stage along with the readings of the microscopeinstrument at those positions, for linearization of image data bypostimaging correction techniques, or for calibration of commandedpositions by the recorded actual (x,y) positions of the scanner forfuture scans, according to conventional techniques, as describedearlier. In the preferred embodiment illustrated in FIG. 9,corresponding to FIG. 4 described earlier, a differential amplifier 40can be electrically connected to receive the position command signal 36and the actual position correction signal 38 to output a correctedcommand signal to the electromechanical actuators in a closed feedbackloop configuration.

An alternate form of a closed feedback loop configuration for use withthe tube scanner of FIGS. 6-8 is as described and illustrated withregard to FIG. 5.

The scanner linearization and calibration system of the invention isadvantageous in that it can be small and relatively inexpensive tomanufacture, and in that it is also possible to achieve an improvedsample stage positioning and imaging accuracy of one part in 100,000,which is an improvement of at least an order of magnitude over thedegree of positioning and imaging accuracy heretofore possible withconventional linearization and calibration systems.

While the system and method of the present invention have been describedin their application to the measurement of displacement of a scanningmember containing a specimen to be scanned by a fixed probe, it is alsoapparent that the invention may be applied to measurement ofdisplacement of a moveable probe as well. In a scanning instrumentincorporating such a probe, the probe is mounted in a moveable carrieranalogous to the arrangement illustrated in FIGS. 1-8, with the positionof the scanning sample stage 18 taken by a probe mounting means. Such aprobe scanning apparatus could be either arranged to scan a sample stagemounted in a fixed fashion to a base member, or in opposition to ascanning stage of the type illustrated in FIGS. 1-8.

More particularly, such an arrangement allows for greater flexibility inthe range and types of scanning that may be accomplished and theinvention offers particular advantages for such an arrangement byproviding increased measurement accuracy over other methods. thusminimizing the errors inherent in the use of piezoelectric actuatorswhen multiple sets of such actuators are used to create relativedisplacement between sample and probe. FIG. 10 is an illustration of aperspective view of such an arrangement, showing the piezoelectricstacks and deflecting members for the two opposing stages. While aparticular arrangement has been illustrated, those skilled in the artwill recognize that other arrangements of actuators and deflectingmembers providing relative motion between the probe and sample, arecontemplated by the invention.

Referring to FIG. 11, sample stage 18 is mounted on a scanning tower 16pivotally attached to a fixed base 12. Piezoelectric actuators 26 areused to move the sample stage relative to the base. Deflecting members30, in this case beams, are mounted between the fixed base and thescanning tower 16, and thereby deflect in response to movement of thetower, and thus the sample stage. Straining gauges 32 are mounted ondeflecting members 30 to provide an output indicating the displacementof the sample stage 18.

Similarly, probe stage 100 contains a probe 102 mounted in a probeholder 104 driven in at least one axis by actuators 106 mounted betweena fixed base 108 and the probe holder 104. In a fashion similar to thepreviously described sample stage actuator and measurement system,deflecting members 110 are mounted between base 108 and holder 104 andequipped with strain gauges 112 to provide an independent measurement ofthe position of probe holder 104 and thus probe 102.

For the sake of clarity, no actuators and deflecting members areillustrated to operate the probe holder 104 or sample stage 18 indirections octagonal to the plane of the actuators illustrated. Inpractise, it is contemplated that one more such actuators and deflectingmembers would be attached between said stages and probe holding tofacilitate vertical motion between said probe 102 and said sample stage18 to perform the measurements required of the instrument.

It should be evident that it would be possible to mount deflectingmembers opposite electromechanical actuators for measuring displacementof a sample stage of a pivot type scanner. It would also be possible tomount a leaf spring deflecting member to a fixed mounting plate, withopposing strain gauges attached, with the other end of the leaf springmounted at right angles to an intermediate solid connecting membermounted to the pivot tower, for either a pivot scanner or tube scannerembodiment. An upright deflecting member with opposing strain gaugesattached could also be connected to a pivot scanner or tube scanner formeasuring displacement of a sample stage. It would also be possible tomount strain gauges to the electromechanical actuators of the pivotingscanner or the electromechanical segments of the tube scanner, or toother types of deflecting elements mounted on or adjacent to the scannerapparatus in configurations similar to those described, to detectdisplacement of the scanner sample stage in three dimensions.

It will be readily apparent from the foregoing that while particularforms of the invention have been illustrated and described, variousmodifications can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

We claim:
 1. A system for linearization and calibration of anelectromechanical scanning apparatus for scanning topography of asample, said system comprising:a fixed mount; a scanner mounted fordisplacement of said scanner relative to said fixed mount; a controllerconnected to said scanner for generating a command signal for a desireddisplacement of said scanner; a deflecting member mounted between saidscanner and said fixed mount adapted to undergo deflection in responseto displacement of said scanner; means attached to said deflectingmember for measuring said deflection of said deflecting member and forgenerating an output deflection signal indicative of an amount ofdeflection of said deflecting member; and closed loop feedback controlmeans for providing a control signal to said scanner derived from saidoutput deflection signal and said command signal.
 2. The system of claim1, wherein said means for measuring said deflection comprises a straingauge mounted to said deflecting member for producing an electricalsignal indicative of the deflection of said deflecting member.
 3. Thesystem of claim 1, wherein said means for measuring said deflectioncomprises a plurality of pairs of strain gauges mounted on opposingsides of said deflecting member, each of said pairs of strain gaugesproducing first and second electrical signals indicative of said amountof deflection due to said displacement, and wherein said first andsecond electrical signals are connected to a differential amplifierhaving an output proportional to the actual displacement of said scannerrelative to said fixed mount from an initial position.
 4. The system ofclaim 1, wherein said deflecting member is formed in a right angle andmounted between said scanner and said fixed mount, and said means formeasuring said deflection comprises first, second and third pairs ofstrain gauges mounted on opposing sides of said deflecting member, eachof said pairs of strain gauges producing first and second electricalsignals indicative of said amount of deflection of said deflectingmember, and wherein each of said first and second electrical signals areconnected to a differential amplifier having an output proportional tothe actual displacement of said scanner in two degrees of freedomrelative to said fixed mount from a position in which the displacementof the scanner is substantially zero and an output in one degree offreedom proportional to the topography of the sample.
 5. The system ofclaim 1, further comprising means for determining an actual displacementof said scanner based upon said output deflection signal, wherein saidclosed loop feedback control means integrates said actual displacementto provide an integrated displacement correction signal, and furthercomprising means for modifying said command signal with said integrateddisplacement correction signal to produce said desired displacement ofsaid scanner.
 6. The system of claim 1, further comprising anelectromechanical actuator electrically connected to said controller andmounted to said fixed mount for displacing said scanner relative to saidfixed mount in response to said command signal.
 7. A system forlinearization and calibration of an electromechanical scanning apparatusfor scanning topography of a sample, said system comprising:a microscopefor producing image data of a sample; a fixed mount for mounting saidmicroscope; a sample stage for said sample; a scanner mounted fordisplacement of said sample stage relative to said microscope; adeflecting member mounted between said scanner and said fixed mountadapted to undergo deflection in response to displacement of saidscanner; means attached to said deflecting member for measuring saiddeflection of said deflecting member and for generating an outputdeflection signal indicative of an amount of deflection of saiddeflecting member; and means for correcting distortions in said imagedata based upon said output deflection signal.
 8. The system of claim 7,wherein said means for measuring said deflection comprises at least onestrain gauge mounted to said deflecting means for producing anelectrical signal indicative of the deflection of said deflectingmember.
 9. The system of claim 7, wherein said means for measuring saiddeflection comprises a plurality of pairs of strain gauges mounted onopposing sides of said deflecting member, each of said pairs of straingauges producing first and second electrical signals indicative of saidamount of deflection due to said displacement, and wherein said firstand second electrical signals are connected to a differential amplifierhaving an output proportional to the actual displacement of said scannerrelative to said fixed mount from an initial position.
 10. The system ofclaim 7, wherein said deflecting member is formed in a right angle andmounted between said scanner and said fixed mount, and said means formeasuring said deflection comprises first, second and third pairs ofstrain gauges mounted on opposing sides of said deflecting member, eachof said pairs of strain gauges producing first and second electricalsignals indicative of said amount of deflection of said deflectingmember, and wherein each of said first and second electrical signals areconnected to a differential amplifier having an output proportional tothe actual displacement of said scanner in two degrees of freedomrelative to said fixed mount from a position in which the displacementof the scanner is substantially zero and an output in one degree offreedom proportional to the topography of the sample.
 11. The system ofclaim 7, wherein said means for correcting distortions in said imagedata comprises:means for determining actual displacement positions ofsaid scanner based upon said output deflection signal; and memory meansfor receiving said actual displacement positions and storing said actualdisplacement positions along with said image data of said microscope atsaid actual displacement positions for linearization of said image data.12. The system of claim 7, further comprising a controller connected tosaid scanner for generating a command signal for a desired displacementof said scanner, and an electromechanical actuator electricallyconnected to said controller and mounted to said fixed mount fordisplacing said scanner relative to said fixed mount in response to saidcommand signal.
 13. A method for linearization and calibration of anelectromechanical scanning apparatus for scanning a sample stage for asample relative to a microscope, said scanning apparatus including afixed mount for mounting said microscope, a scanner mounted fordisplacement of the scanner relative to said fixed mount, a deflectingmember mounted between said scanner and said fixed mount, and means formeasuring deflection of the deflecting member, the steps of the methodcomprising:scanning said sample stage relative to said microscope;generating a command signal for scanning said sample stage a desireddisplacement; displacing said sample stage relative to said microscopein response to said command signal; measuring said deflection of saiddeflecting member and generating an output deflection signal indicativeof an amount of deflection of said deflecting member; and providing aclosed loop feedback control signal to said scanner derived from saidoutput deflection signal and said command signal.
 14. The method ofclaim 13, further comprising the steps of determining an actualdisplacement of said scanner based upon said output deflection signal,integrating said actual displacement to provide an integrateddisplacement correction signal, and modifying said command signal withsaid integrated displacement correction signal to produce said desireddisplacement of said scanner.
 15. The method of claim 13, wherein saidmeans for measuring said deflection comprises a strain gauge mounted tosaid deflecting member for producing an electrical signal indicative ofthe deflection of said deflecting member, said scanner further comprisesa probe for scanning the topography of the sample, and wherein theoutput of said strain gauge is used to measure the position of the probeover the sample.
 16. A method for linearization and calibration of anelectromechanical scanning apparatus, said electromechanical scanningapparatus including a microscope for producing image data of a sample, afixed mount for mounting said microscope, a sample stage for saidsample, a scanner mounted for displacement of said sample stage relativeto said microscope, and a deflecting member mounted between said scannerand said fixed mount, the steps of said method comprising:generating acommand signal for a desired displacement of said scanner; displacingsaid scanner relative to said fixed mount in response to said commandsignal; measuring said deflection of said deflecting member andgenerating an output deflection signal indicative of an amount ofdeflection of said deflecting member; and correcting distortions in saidimage data based upon said output deflection signal.
 17. The method ofclaim 16, wherein said step of correcting distortions in said image datacomprises:determining actual displacement positions of said scannerbased upon said output deflection signal; and linearizing said imagedata based upon said actual displacement positions.
 18. The method ofclaim 16, wherein said scanner further comprises a probe for scanningthe topography of the sample, and wherein output deflection signal isused to measure the position of the probe over the sample.